1. Field of the Invention
The invention relates to multiphase reactors with exothermal heat of reaction and, more particularly, to an arrangement for cooling the reactors.
2. Description of the Prior Art
Conventional hydrogenation reactors in the sump phase, which are operated at high temperatures and pressures, in most cases, PG,3 have a ceramic lining to keep the load-bearing steel jacket at a low temperature to maintain the strength of the jacket. As a result of the temperature gradient which is established in the reactor wall, heat flows from the contents of the reactor to the environment. This waste heat represents a heat loss. However, the heat of reaction of the reactor products, for example, during coal hydrogenation, is significantly greater than the heat loss which is released through the reactor walls. Because of this, additional cold gas must be introduced into the reactor at various points to extract the excess heat of reaction from the reactants, thus establishing an approximately isothermal temperature profile of the reactor contents.
In sump-phase reactors, for example, for coal hydrogenation, the reaction heat to be extracted differs considerably along the reaction path. After the introduction of the reaction components of reaction into the reactor, the heat of reaction is initially required to heat up these reaction components. To avoid an increase above the optimal reaction temperature in the subsequent reaction phase, the excess heat of reaction must be extracted.
As a result of the decomposition of reaction products, this heat of reaction decreases as the reaction proceeds, resulting in different introductions of cold gas along the reaction path.
In spite of controlled local introductions of cold gas along the reaction path, it is not possible, however, to achieve a desired isothermal temperature profile of the reactor contents. It is known from test results in hydrogenation reactors in the sump phase that the influx of cold gas produces local zones cooled below the desired temperature. If the temperature is below the optimal reaction temperature, the chemical conversion in these zones decreases significantly. In addition, the cold gas fed in--a hydrogen-rich reaction gas, in the case of the hydrogenation of coals, tars, heavy oils, etc.--is absorbed to a lesser extent by the reactive liquid/solid phase at this low temperature, which thus has a negative influence on the chemical reaction in the sump phase.
A cold gas injected along the reaction path also has the disadvantage that it can only be used to a limited extent for chemical conversion as a reaction gas with a reduced hold time. Cold gas injection also requires a rather large gas circuit with increased compression capabilities.
As a result of the bubble column flow, the increased gas velocity decreases the density of the liquid/solid phase in the rear reactors and reduces the chemical product formation.
The comparatively large quantities of cold gas which have heretofore been customary also have a significant adverse effect on the thermal efficiency of the overall process, since the energy losses are high if cold gas is used to extract the heat of chemical reaction.
It is known, as in German Democratic Republic (DDR) Patent Specification No. 54 994, which is incorporated herein by reference, that the heat of reaction can be extracted through the reactor wall in a reactor with "floating bubbles", whereby the reaction heat is economically used to heat the charge materials in the jacket space of the reactor, and the cold gas injection described above is no longer necessary.
In this apparatus, on the pressure side of the gas compressor, a quantity of cold gas is extracted as a partial flow from the gas circuit and introduced by means of a regulating mechanism into the reactor annulus. As it flows through the annulus, this gaseous partial flow is heated to approximately the reaction temperature and, at the same time, provides for the necessary pressure equalization.
With regard to high pressure reactors with a mixture of gaseous, liquid, and solid reaction partners, the process described in German Democratic Republic Patent Specification No. 54 994 is not applicable, because of the existence of a direction connection disposed between the annulus and the inner chamber. Through this direction connection, reaction products containing solid matter can get into and plug up the annulus, either partly or completely (carbonization during hydrogenation in the sump phase), for example, there are pressure fluctuations as a result of operational disruptions. That would mean that a uniform cooling of the outer, load-bearing reactor jacket could not be assured.
With the process described above, it should be recalled that the partial flow extracted from the gas circuit must be fed through a regulating mechanism into the annulus of the reactor. This regulating mechanism, however, can represent a source of problems for the entire process.
Therefore, in another proposal, the "floating bubble" reactor principle was adapted to the requirements of the three-phase sump-phase hydrogenation, described in German Pat. No. DE 33 23 885 A 1, incorporated herein by reference. Here, however, it is not possible to achieve an isothermal temperature profile in the reactor, since the above-mentioned different heats of reaction along the reaction path cannot be extracted as desired through the reactor wall. Even with the above-mentioned German Democratic Republic (DDR) Patent Specification No. 54 994 process, the heat of reaction cannot be extracted as desired to achieve an isothermal temperature profile in the reactor.
The other common industrial method of producing an isothermal temperature profile, by means of agitators or equipment installed in the reaction chamber, cannot be used in the case of the three-phase sump-phase hydrogenation because of the dangerous formation of solid deposits on the equipment.
In industry, it is known that the principle of the loop-type bubble column reactor can be used to achieve an isothermal temperature profile in the reactor.
In this method, by means of a guide tube introduced vertically in the reactor, an intensive re-mixing of the reaction products is achieved, which causes a temperature equalization. For the extraction of the heat of reaction, the guide tube can be designed as a cooling jacket in the interior of the reactor, as in German Pat. No. DE-PS 859 444, which is incorporated herein by reference. In coal hydrogenation, however, a complete physical remixing, especially of the specific heavier reaction partner, is undesirable.
The recycling of the heavy or non-decomposable products (asphalts and pre-asphalts) in a loop-type bubble column has a negative effect on the chemical reaction which is similar to that of the external recycling of the high-asphalt sludge from the output of the last reactor to the input of the first reactor. In another process, with a loop-type bubble column and partial external recycling of products, the products with low boiling points (asphalts and pre-asphalts) are recirculated, as in German Pat. No. DE-PS 926 846, which is incorporated herein by reference. The latter two processes also have the disadvantage, as far as coal hydrogenation is concerned, that equipment installed in the reactor, for example, vertical guide tubes and an internal cooling system, especially where it presents physical flow obstructions, can frequently lead to deposits and carbonizations.
Some examples of gas cooling of other types of non-analogous reactors are found in U.S. Pat. Nos. 4,346,758, issued on Aug. 31, 1982; 4,158,637, issued on June 19, 1979; 4,045,285, issued on Aug. 30, 1977; and 4,021,298, issued on May 3, 1977, all of which are incorporated herein by reference.
Some examples of refining are provided in the following U.S. Pat. Nos. 4,485,003; 4,473,460; 4,444,698; 4,410,646; 4,406,744; 4,331,530; 4,221,654; 4,191,539; 4,123,502; 4,099,933; 4,057,402; 4,036,731; 3,953,180; 3,950,244; 3,926,775; 3,884,649; and 3,862,108. All of the aforementioned patents are incorporated herein by reference.